It has been documented that there is a group of righteous people called "The Nistarim". I am not referring to the lammed vav tzaddikim of the Gemara (Sanhedrin 97b, Sukkah 45b). Rather, a mystical brotherhood whereby the leader goes by the name Baal Shem (see here for wiki article and here for chabad article).

My question is twofold:

What practices did/does this group engage in?

Although all the info I could gather online seems to suggest this group formed around the time of the emergence of Hassidut, I have been told by a particular Chassidic Rebbe that his tradition is that this group dates back to the times of Rabbi Akiva, and the purpose of their continued efforts is to bring back prophecy to the Jewish people through meditative techniques passed down from generation to generation, dating back to Talmudic times, in an attempt to usher in the Messianic era. Does anyone know of any material on this subject?

Thank you @ShmuelBrin these seem to suggest that the group did not exist before the onset of chassidut, if you find any that claim as suggested in question 2 above, I would be very interested
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AKayserJun 12 '14 at 19:40

Hi Akayser. I know it's "only" Wikipedia but they do have an article on this group: en.wikipedia.org/wiki/Tzadikim_Nistarim. I remember, but don't have a source, of the concept of there always being 36 people whose identities are unknown to all including each other. Their job is through mystical means to keep the world in existence. Check out the wiki article for more details. Very intriguing!
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JJLLJun 12 '14 at 22:44

@JJLL this is referring to the 36 righteous people always present in the world, otherwise known as the lammed vav tzaddikim I quoted above in the question. My question was specifically not referring to them, but rather to another group called the nistarim
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AKayserJun 12 '14 at 23:17